1. Field of the Invention
This invention relates to a solid electrolytic capacitor such as tantalum capacitor or aluminum capacitor. More specifically, the present invention relates to a package type solid electrolytic capacitor which incorporates a safety fuse within the package.
2. Description of the Related Art
Solid electrolytic capacitors such as tantalum capacitors or aluminum capacitors are known to provide a large capacitance while realizing a great size reduction. For this reason, solid electrolytic capacitors are used in various applications.
Typically, a solid electrolytic capacitor has a capacitor element and a resin package enclosing the capacitor element for protection, as disclosed in Japanese Patent Application Laid-open No. 5-67523 (Laid-open: Mar. 19, 1993) for example. The capacitor element includes a capacitor chip, and an anode wire partially inserted into and partially projecting from the chip. The capacitor chip may be a compacted and sintered mass of tantalum powder which is treated to have a dieletric layer and a solid electrolyte layer. The electrolyte layer serves as a cathode of the capacitor element, whereas the anode wire acts as an anode.
The anode wire may be directly connected to an anode lead by welding for example, whereas the capacitor chip (solid electrolyte layer) may be electrically connected to a cathode lead through a safety fuse. The fuse may be designed to be melt-cut upon passage of an overcurrent and/or by an excessive temperature.
With the prior art fused capacitor described above, when the safety fuse is melt-cut, a melted portion of the fuse undergoes a considerable volmetric increase. Such a volmetric increase may be allowed to a certain extent by enclosing an intermediate portion of the fuse in an elastic insulating resin member. However, if the volumetric increase is too large, the molten metal may leak out of the resin package, consequently solidifying outside the resin package. As a result, the leaked portion of the fuse may cause shorting or other electrical troubles on a circuit board on which the capacitor is mounted.
Further, since the resin package is not light-permeable, it is impossible to visually recognize a breakdown of the safety fuse unless a melted portion of the fuse leaks out of the resin package.